1. Field of the Invention
The present invention relate to a perpendicular magnetic recording medium, and more particularly, to a bit patterned medium where bits, which are units of data, are isolated in the form of islands.
2. Description of the Related Art
Since hard disk drives (HDDs) using a magnetic recording medium have high capacity and high speed access, HDDs are used as storage media for various digital devices as well as computers. The capacity of magnetic recording media is determined by tracks per inch (TPI), which is track density in the rotational direction of a disk, and by bits per inch (BPI), which is bit density on tracks. One of the most popular magnetic recording media, continuous magnetic recording media where bits are not physically isolated have limitations in increasing TPI and BPI by reducing a bit size or a track pitch. This is because, when a bit size or a track pitch is reduced below a limit, noise increases due to magnetic interaction between adjacent bits and recording stability degrades drastically.
In bit patterned media where bits, which are units of data, are isolated in the form of islands, the bits are formed along tracks of a rotating disk and spaces between the patterned tracks or bits are empty or filled with a nonmagnetic material. Since there is no interaction between adjacent bits, the bit patterned media can achieve high recording density.
However, one requirement for bit patterned media applications is the minimization of a switching field distribution of bits. Factors affecting the switching field of each bit include the dimension and magnetic characteristics of each bit, and the magnetization directions of neighboring bits. The dimensions and magnetic characteristics of bits may be uniform. A difference between the dimensions or magnetic characteristics of bits can be kept within allowable ranges by controlling manufacturing processes. However, a switching field difference due to magnetostatic interaction between adjacent bits cannot be reduced by controlling manufacturing processes. In order to reduce a switching field difference, it is necessary to reduce a bit size or a saturation magnetization (MS). However, in such a case, output is reduced, thereby causing another problem.